Well fracturing method using explosive slurry

ABSTRACT

A method of fracturing a geological formation adjacent a well bore is described, comprising injecting a free-flowing explosive slurry, which is nondispersible in well fluids over a time period required to fracture the formation and thus retains its initial density until fracturing and which contains a granular explosive which is nonhygroscopic and insoluble in the dispersive medium of the slurry, into the well bore directly adjacent the formation to be fractured, so that the slurry cannot contact fluids in the well bore before reaching the formation, then placing a detonating device in the slurry and detonating it to explode the slurry. The explosive slurry used in the method is an even dispersion in an inert fluid dispersive medium of a granular solid explosive, which is an organic nitro compound of high explosive power and which is insoluble in the dispersive medium, to which is added a gelling agent for maintaining the solid explosive evenly dispersed throughout the fluid medium under conditions of temperature and pressure encountered in well fracturing.

United States Patent [72] Inventors David A. Fletcher Mesa; Leonard N.Roberts, Scottsdale, Ariz. 21] Appl. No. 716,056 [22] Filed Mar. 26,1968[45] Patented Feb. 9, 1971 [73] Assignee Talley-Frac Corporation Pryor,Okla. a corporation of Delaware [54] WELL FRACTURING METHOD USINGEXPLOSIVE SLURRY 8 Claims, 4 Drawing Figs.

[52] US. Cl 166/299, 149/92, 149/93 [5]] 1nt.Cl E21b 43/26 [50] Field ofSearch 166/36, 42.1,153,156,299z102/22, 23; 86/203 (Inquired); 149/2,92, 93 (Inquired) 56] References Cited UNITED STATES PATENTS 1,627,9915/1927 Owen 102/23 2,630,179 3/1953 Brown... 166/156X 2,708,876 5/1955Nowak 102/23X 2,867,172 1/1959 Hradel l49/92X 2,892,405 6/1959 Chesnut166/36 2,892,406 6/1959 Hradel et a1. 102/23 3,147,163 9/1964 Griffithet a1. 149/92X 3,191,678 6/1965 Hinson 166/36 OTHER REFERENCESZimmerman, 0. T., et a1. Handbook of Material Trade Names, SupplementIV. Dover, NH, 1nd. Research Serv., 1965, p 48. (Copy in Group 165).

Primary Examinerlan A. Calvert Attorney-Pennie, Edmonds, Morton, Taylorand Adams ABSTRACT: A method of fracturing a geological formationadjacent a well bore is described, comprising injecting a freeflowingexplosive slurry, which is nondispersible in well fluids over a timeperiod required to fracture the formation and thus retains its initialdensity until fracturing and which contains a granular explosive whichis nonhygroscopic and insoluble in the dispersive medium of the slurry,into the well bore directly adjacent the formation to be fractured, sothat the slurry cannot contact fluids in the well bore before reachingthe formation, then placing a detonating device in the slurry anddetonating it to explode the slurry, The explosive slurry used in themethod is an even dispersion in an inert fluid dispersive medium of agranular solid explosive, which is an organic nitro compound of highexplosive power and which is insoluble in the dispersive medium, towhich is added a gelling agent for maintaining the solid explosiveevenly dispersed throughout the fluid medium under conditions oftemperature and pressure encountered in well fracturing.

PATENTEI] FEB 919m 3.561.532

SHEET 1 BF 2 H6. FIG, 2

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INVENTORS DAVID A. FLETCHER LEONARD N. ROBERTS ATTORNEYS PATENTEUFEB9|97| sum 2 BF 2 PUMP 3% WATER FIG. 3

FIG. 4 "J INVENTORS DAVID A. FLETCHER LEONARD N. ROBERTS ATTORNEYS WELLFRACTURING METHOD USING EXPLOSIVE SLURRY BACKGROUND OF THE INVENTION ofa well which has substantially ceased to produce oil, water or gas.While the explosive slurry herein described is useful for otherapplications, such as mining, the present application is concerned withits use in well fracturing. To bring in a well, after it has beendrilled, it is usually necessary to increase the porosity of theproducing formation, or pay zone, to stimulate flow in the well. Thishas commonly been done by shooting" the well with a nitroglycerine orTNT charge; acidizing, in certain types of formations; or hydraulicfracturing. Similarly, when the pay zone of a formerly productive wellhas ceased to produce, hydraulic or explosive fracturing of the pay zoneis used to bring the well back into production. The purpose offracturing is to increase the porosity of the'productive formation,permitting oil (water or gas) to flow into and up the well bore.

Explosive fracturing was originally carried out by placing anitroglycerine charge in the well bore and detonating it. While liquidnitroglycerin has been used for this purpose for many years, it isextremely shock sensitive and difficult to handle and transport; it istoo sensitive for example, to be pumped or poured into a well, and mustbe carefully placed there. Solid explosives have also been used, butthey are difficult to get into the well bore and cannot made to fill thebore, let alone the productive formation, and consequently are oflimited effectiveness in increasing the porosity of the formation.

Liquid explosives other than nitroglycerine have also been tried but ingeneral have not been successful because of the instability of theexplosives or explosive mixtures used.

2. History of the Prior Art To overcome these drawbacks, experimentshave been conducted since the early l950's with slurry explosives, whichare dispersions of solid explosives or of one or more constituents whichtogether constitute an explosive, suspended in water or some otherdispersive medium. Slurry explosives have the advantage of being able toconform to and thus more readily fill the bore hole, resulting ingreater explosive power. Fracturing may be enhanced, moreover, bypumping the slurry under pressure directly into the formation to befractured, thereby improving the effectiveness of the charge inincreasing porosity. However, to the inventors knowledge, nocommercially successful slurry explosive for well fracturing has yetbeen produced; they have been for the most part either too unstable,leading not infrequently to accidents in the field or, more often, havebeen incapable of consistent and predictable detonation.

The bulk of slurries developed to date, many of which include gellingagents, have used ammonium nitrate as a major constituent. Such slurriesare generally unpredictable in their detonation characteristics, andoften will not detonate at all. One reason for this is believed to bethat ammonium nitrate is relatively hygroscopic and water soluble. Whenexposed to fluids commonly found in the well bore, the slurry issufficiently diluted to render it nondetonatable. Some attempts havebeen made to overcome this difficulty by using shaped charges fordetonation, but even this has not proven entirely successful. Further,shaped charges are relatively difficult to use, and are thereforeundesirable.

One proposed method which appears to have avoided at least this drawbackinvolved sealing slurry in polyethylene bags, and placing the sealedbags in the bottom of the well bore adjacent the formation to befractured, to prevent the slurry contained in the bags from beingdiluted before detonation. However, aside from the relative difficultyof placing the bags in the well bore, substantially less explosive forcecan be developed at the formation with this method than with anunconfined slurry such as is used in the present invention. Some workhas also been done with propellant type (as opposed to explosive type)liquids and slurries; however, these have to a large extent provedunstable and thus are not suited for commercial application.

Some of the slurries developed to date are dispersions of granular solidexplosives in water or hydrocarbons; however, tests of such slurrieshave been largely unsuccessful, principally due to detonationdifficulties, even though a booster charge is used. The difficultyencountered in detonating such slurries is exemplified by U.S. Pat. No.2,867,l72 to Hradel, which points out the necessity for extensive safetyprecautions in using conventional detonators, which had to be intimatelymixed with the basic explosive in the bore hole, and in particular thedifficulty of achieving detonation where the slurry was to bepressurized into the formation. As a solution, Hradel proposed that acomplicated arrangement of shaped charges be set in the bore hole todetonate the slurry, which in particular was a dispersion of RDX,Composition B, ammonium nitrate or similar materials in a dispersivemedium such as water. The patent states that the particles of explosivein the slurry are trapped in fissures in the formation, forming acontinuous phase of explosive material which may then be detonated bythe arrangement of multiple shaped charges (see FIG. 2'). Assuming thatthis procedure works, it is commercially highly unsatisfactory due tothe necessity of the complex shaped charge detonation procedure. Thepatent appears to recognize, moreover, that the explosive constituentswere capable of dissolving in the dispersive medium, or of settling out(col. 3 which may have been, at least in part, the reason why themultiple shaped charge detonation procedure was thought to be required.

SUMMARY OF THE INVENTION This invention is based on the discovery thatby providing a slurry explosive which is nondispersible in well fluidsover a time period required to fracture the formation and thus retainsits initial density until fracturing and which contains a granularexplosive which is nonhygroscopic and insoluble in the dispersive mediumof the slurry, and by injecting such slurry explosive into the well boredirectly adjacent the formation it is desired to fracture, so that theslurry cannot contact oil or water in the well bore (and thus beemulsified, leached out or otherwise diluted) before reaching theformation, it is possible to fracture a well with complete safety, atthe same time achieving consistent and reliable detonation.

Preferably, the slurry is injected into the well bore directly adjacentthe formation to be fractured by pouring it through a tube extendingfrom the surface down through the well bore to the formation, which tubeis provided at its lower end with a one-way valve for permitting flowfrom the tube into the well bore while preventing flow in the reversedirection. The slurry is thus placed in the well directly at theformation, precluding any chance of its being diluted or otherwiseadversely affected by well fluids on the way down the well bore.

The slurry used in this method must be nondispersible in well fluidsover a time period (usually at least a few hours) required to fracturethe formation, so that it retains its initial density until fracturing,and contains a granular solid explosive which is nonhygrosc'opic andinsoluble in the dispersive medium of the slurry. It comprises an inertfluid dispersive medium, one or more granular solid explosives which areorganic nitro compounds of high explosive power and which are insolublein the dispersive medium, and a gelling agent for maintaining thegranular solid explosive evenly dispersed throughout the dispersivemedium under conditions of pressure and temperature existing in wellfracturing.

Preferably, the slurry is composed of a dispersive medium such as water,kerosene or alcohol having dispersed therein, in granular form, RDX,PETN, HMX, TNT or a mixture of the foregoing, as well as a gelling agentcompatible with the particular dispersive medium and explosive andcapable of maintaining an even dispersion of the latter under conditionsof temperature and pressure existing in well fracturing.

In a particular preferred embodiment of the invention, the slurry is adispersion of about between 45 percent and 70 percent RDX in water, withabout 0.5 percent Carbopol 941, a gelling agent.

BRIEF DESCRIPTION OF THE DRAWINGS Particular embodiments of theinvention will be described in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic sectional view of a well bore, the upper portionof which contains a cement casing and which extends into a potentiallyproductive formation;

FIG. 2 is a schematic sectional view showing a tube in the well bore ofFIG. 1 extending into the formation;

FIG. 3 shows the well bore of FIGS. 1 and 2 with a pump connected to thetube for pressurizing slurry into the formation; and

FIG. 4 shows the well bore of FIGS. 1-3 with a packing plug seated atthe lower end of the casing above the formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Explosive Slurry The explosiveslurry, according to the invention, is composed of a dispersive medium,a granular solid explosive evenly dispersed therein, and a gelling agentfor maintaining an even dispersion of the explosive throughout thedispersive medium.

The dispersive medium may be water, or any of a number of suitablehydrocarbons or hydrocarbon derivatives such as hexane, kerosene, ordenatured alcohol. It must be inert, and capable of desensitizing thegranular explosive, and must be of sufficient density so that the slurryis substantially more dense than fluids which may be encountered in thewell bore. Water in particular is an excellent and inexpensivedesensitizing agent. This assures that the slurry will settle on thebottom of the well bore, causing any other fluids present to rise aboveit. The dispersive medium must also be compatible with the particularexplosive and the particular gelling agent used; will be chosen to becompatible with the dispersive medium and explosive.

The granular solid explosive may be any one or more organic nitrocompounds of high explosive power, preferably about equal to or greaterthan that of TNT. It is essential that the explosive be insoluble in thedispersive medium and that it be nonhygroscopic. While most organicnitro compounds are to a minor extent soluble in the dispersive mediamentioned above, as used herein the expressions insoluble andnonhygroscopic" are intended to mean that the explosives described areessentially insoluble or nonhygroscopic, and consequently aredetonatable.

Preferred organic nitro compounds include RDX (cyclotrimethylenetrinitramine), HMX (cyclotetramethylene tetranitramine), and PETN(pentaerithrytol tetranitrate). TNT may also be used. To assure that thesuspended particles of explosive are able to pass into and throughfissures in the formation, the explosive should have a grain size whichis preferably below about 100 mesh, for example, 200 microns.

The gelling agent must be capable of maintaining an even dispersion ofthe granular explosive under conditions of temperature (up to about 150F.) and pressure (up to about 5,000 psi.) encountered in wellfracturing, must render the slurry nondispersible in well fluids over atime period required to fracture the formation, so that it retains itsinitial density until fracturing, and must be compatible with theparticular explosive and dispersive agent used. The gelling agent ordispersing agent may be any one of such agents manufactured under thetrademark Carbopol (a trademark of B. F. Goodrich Chemical Company, NewYork for carboxy vinyl polymers of extremely high molecular weight whichare water soluble and supplied in acid form for use as thickening.dispersing, suspending and emulsifying agents) or any one of the fattyacid or protein colloid gelling agents. It may be a protein-based gel,an aluminum silicate or any one of the metallo-organic compoundssuitable for this purpose. Generally the gelling agent will constitutebetween about 0.5 and 3 percent by weight of the slurry.

The proportions of granular explosive and dispersive medium used willdepend upon the particular conditions involved. However, sufficientexplosive must be present to achieve detonation, whereas if too muchexplosive is present, the slurry will not be free-flowing and will betoo viscous to pump or pour. Further, settling tends to occur in lessviscous slurries unless a higher proportion of gelling agent is present.In an RDX-water system, RDX should constitute about between 45 and 70percent by weight of the slurry. Within this range, the material isdetonatable and free flowing; below this range the slurry is insensitiveto detonation and above this it is too viscous.

In an RDX-kerosene or RDX-denatured alcohol slurry, the RDX mayconstitute between about 3570 percent by weight of slurry. Preferably,the explosive constitutes about between 55 and 65 percent by weight ofslurry. The slurry may be prepared in any of a number of ways; apreferred method, for example in an RDX-water slurry, is to weight upthe dispersive medium, granular explosive and gelling agent in thedesired porportions. A dual-impeller mixer is placed in the dispersivemedium so that a vortex is formed and the gelling agent is slowly addedinto the vortex. The mixer shaft is then repositioned to eliminate thevortex and mixing is continued until a thin hazy dispersion is achieved.Assuming that the gelling agent in this case is Carbopol 941 or asimilar agent which is commercially available in acid form, a base suchas 10 percent sodium hydroxide solution is then added until the pHreaches between 5 and 7, at which point a gel immediately forms. Thegranular explosive is then added, continuing agitation until a completeand even dispersion is obtained.

Specific embodiments of free-flowing explosive slurries according to theinvention are illustrated in the following examples, wherein all partsare by weight.

EXAMPLE I Parts RDX 48 Water 51. 5 Carbopol 941 0. 5

EXAMPLE II Parts HMX 60 Water 39 Hydrated silica dispersing agent(Cab-O-Sil) 1 EXAMPLE III Parts RDX 49 Ethyl alcohol (denatured) 49Carbopol 941 2 EXAMPLE IV Parts PETN 50 Water 49 Carbopol 941 1 In anonaqueous slurry, finely powdered metals may be added to enhance theexplosive power of the slurry.

2. Well Fracturing Method The well fracturing method according to theinvention comprises injecting a slurry explosive such as is describedabove into the well bore directly adjacent the formation to be fracturedsuch that the slurry cannot contact fluids in the well bore beforereaching the formation, placing a detonating device containing a highexplosive charge within the slurry in the well bore, and detonating theexplosive charge.

It is essential in well fracturing by this method that the slurry benondispersible in well fluids over a time period required to fracturethe formation (i.e., the time during which the slurry is in contact withwell fluids), so that it retains its initial density until fracturing,and that the slurry be injected into the well directly adjacent theformation to be fractured. While dilution of the solid explosive in thedispersive medium is necessary to desensitize it, and thereby to renderits use safe, maintenance of the concentration of the explosive isessential to proper detonation. If the explosive is diluted by wellfluids, such as water (which may for example be somewhat acidic), orsettles out, detonation will not occur. An even dispersion is necessarybecause the detonating device carrying the high explosive charge must besurrounded by the slurry in order to detonate it.

Thus, in certain instances in which the slurry has been poured directlyinto the well bore (as opposed to being injected through a tube to theformation), well fluids have leached sufficient gelling agent out of theslurry to cause settling out of the explosive and, consequently,detonation failure. Detonation failure may also occur, even thoughdirect injection is used, if the slurry is dispersible in fluids in thewell bore at the formation in a time period less than that required forfracturing by this method. Detonation failure can be consistentlyavoided under all conditions only by using the slurry and methoddescribed herein.

As shown in FIG. 1, a well bore extends from the surface 11 into apotentially productive formation 12 containing fissures 13. A casing 14extends from the surface to a level just above the formation 12 and isbacked by a cement lining 15. The well bore in the formation is uncased.

The method may be used to fracture a formation adjacent a casing in awell, say, with several productive formations, but as with anyfracturing procedure of this type, damage to the easing will resultwhich creates substantial debris upon fracturing and must be repairedafterwards. To fracture a formation at a level above the bottom of thewell bore, a bridge plug or packing plug is placed at the lower end ofthe formation to be fractured. Similarly, if it is desired to preventdownward fracturing, for example because of a water zone below the payzone, the bottom of the well bore may be filled with sand beforeinjecting in the slurry,

Before fracturing, the well bore should be cleaned of sludge, paraffinand the like by well-known techniques. Then, as illustrated in FIG. 2, atube 16 is placed into the well extending from the surface to theformation. Tube 16 is provided at its lower end with a one-way valve 17for permitting flow from the tube into the well bore while preventingflow in the opposite direction, from the well bore into the tube.

One-way valve 17 is a float valve comprising a constricted orifice 18formed in the tube, and a spherical float shoe 19 forming the valveclosure, suspended directly below and slightly spaced from the orificeon a spring 20 which rests on a shelf in the lower end of the tube.Other suitable one-way valves may be used.

An annular plug 22 is placed at the lower end of the casing to seal offthe annular portion between tube 16 and the casing. Where the lowerportion of the well bore is filled with fluids, the packing plug shouldnot be sealed, however, until the slurry has been loaded into the wellbore, as will become apparent. The slurry may then be poured into thetop of the tube 16, either directly or through a tube connected to acontainer of slurry, for example, or the slurry may be pumped into thetube. By this means, the slurry is injected into the well bore directlyat the formation 12 to be fractured, and is prevented from contactingfluids in the well bore before reaching the formation. Note that nofluid from the bore is permitted to enter the tube due to one-way valve17. As the slurry fills the bottom of the well bore, since it issubstantially more dense than the fluid in the well bore, such fluids(usually water and/or oil) are displaced above the slurry and flow pastpacking plug 22 up into the well bore.

As shown in FIG. 3, when the desired amount of slurry has been placed inthe well bore a wiper plug 23 is inserted into the top of tube 16 andthe tube is then connected through a high pressure pump 24 to a sourceof, say, water. Packing plug 22 is then seated by conventional means toseal off the portion of the well bore adjacent the formation. The slurrybelow wiper plug 23 is then driven downward by the wiper plug under pumppressure, forcing the slurry in the tube and in the bore hole intofissures 13.

In some cases, it may be desired to hydraulically fracture the formationbefore explosively fracturing it. This may be done using the explosiveslurry as a hydraulic fracturing fluid, merely by providing enoughpressure at pump 24 to hydraulically fracture the formation.

The packing plug 22 is then unseated and removed along with the tube 16from the bore hole. The level of the slurry in the bore may then bechecked by lowering a temperature sensing device on a cable (not shown)into the well and noting the length of cable paid out when thetemperature sensing device reaches the slurry. This point is easilydeterminable, as the slurry temperature is substantially lower than thatof residual well fluids, which are usually at least 120 F. a l,000 feetbelow the surface. A detonating device 24 containing a timer and a highexplosive charge is then lowered into the well on a wire cable so thatit is submerged in the slurry, and permitted to drop to. the bottom ofthe well, still remaining completely surrounded by the slurry. The highexplosive charge may be any suitable high explosive, such as TNT, and isincluded in the detonating device along with the timer (not shown) forpresetting the device to explode after a predetermined interval.

A packing plug 25 (FIG. 4), commonly referred to as a bridge plug isthen placed at the lower end of the casing to seal .off the productiveformation and protect the casing, and the well bore above packing plug25 is filled with fluid to maintain a static pressure above theexplosion. At the end of the predetermined interval, the detonatingdevice is detonated by its internal timer, causing the slurry toexplode. Bridge plug 25 may then be removed from the well and the debrisresulting from the explosion cleaned out, after which time the well isready for production.

The particular amount of slurry used for any given application willdepend upon the nature of the well, the character of the formation to befractured, and the extent of fracture desired, and may be different foreach well. In general, it has been found that between and 50,000 poundsof slurry is suitable for most applications, and generally between 500and 5,000 pounds will be required.

The following examples illustrate particular embodiments of theinvention.

EXAMPLE V A generally productive well having a productive formation atabout 2,000 feet and which had substantially ceased to produce wascleaned using conventional techniques. A water zone was known to exist ashort distance below the pay zone, and in order to prevent downwardfracturing into the water zone approximately 30 feet of sand was loadedinto the bottom of the well bore. A tube with acne-way valve at itslower end was then inserted through the well bore into the formation,and an annular packing plug was lowered about the tube to the lower endof the well casing, just above the level of the formation. Slurry havingthe composition described in example I above was poured down through thetube into the formation. 4,200 pounds of slurry were used, after which awiper plug was sent under pressure through the tube, so that about 25percent of the slurry was pushed back into the formation. The tube andpumping equipment were then removed and the slurry level in the borehole checked with a temperature sensing device. A TNT detonating deviceset for 2-hours delay was then lowered on a wire line into the slurry,and the wire line reeled back. A bridge plug was then seated at thelower end of the casing, and the well bore above it was filled withwater. it was ascertained before setting the bridge plug that the wellbore was filled with water below the level of the plug, above theslurry. After detonation, the bridge plug was removed and the resultantdebris cleaned out.

EXAMPLE VI The method of example V was carried out, except that no sandwas placed in the bore hole, since no water zone was known to existbelow the pay zone. While a packing plug was used, it was not sealed, sothat when pressure was applied behind the wiper plug, well fluids raisedabove the slurry merely rose in the bore hole. Consequently, it isestimated that only about -10 percent of the slurry flowed back into theformation. l,200 pounds of the slurry of example 1 above were detonatedin the bore hole, and approximately an 800 percent increase inproduction was determined; the well is continuing in production at thisrate.

EXAMPLE VII The method of example V] was carried out except that 800pounds of the slurry of example [11, above, were used. It is estimatedthat approximately 5 percent of the slurry flowed into the fonnation.

it will be appreciated by those skilled in the art that the exemplaryembodiments described above may be modified and still remain within thescope and spirit of the invention, which is limited solely in accordancewith the following claims.

We claim:

1. A method of fracturing a formation adjacent a well bore with a slurryexplosive formed of nonhygroscopic granular solid explosive evenlydispersed throughout a dispersive medium in which it is insoluble andcontaining a gelling agent,

which slurry is nondispersible in well fluids over a time periodrequired to fracture the formation and thus capable of retaining itsinitial density until fracturing, comprising:

placing into said well bore a tube extending from the surface to saidinformation and provided at its lower end with a one-way valve forpermitting flow from the tube into the well bore while preventing flowfrom the well bore into the tube; placing a packing plug in the wellbore about said tube above said formation for sealing off that portionof the well bore adjacent the formation; injecting said slurry throughthe tube and one-way valve into the well bore, leaving a substantialamount of slurry in said tube; inserting a wiper plug into said tube andforcing the slurry therein under fluid pressure through the tube to pressurize the slurry into the formation and then removing said tube andpacking plugmam the well bore;

lowering into said slurry, in the well bore, a detonating devicecontaining a high explosive charge;

placing a packing plug in the well bore above said formation and fillingthe well bore above the slurry and above the packing plug with fluid,for maintaining static pressure above the formation during theexplosion; and

detonating the high explosive-charge to explode the slurry.

thereby fracturing said formation.

2. A method as defined in claim 1 wherein'the detonating device includesa timer for detonating the high explosive charge after a presetinterval, and detonation of the high explosive charge is initiated bysaid timer.

3. A method of fracturing a formation adjacent a well bore with a slurryexplosive consisting essentially of a fluid dispersive medium capable ofdesensitizing a granular explosive dispersed therein; one or moregranular solid explosives which are organic nitro izompounds of highexplosive power and which are nonhygroscopic and insoluble in thedispersive medium evenly dis rsed throughout the dispersive medium;

and a gelling agent or maintaining the granular solid explosive evenlydispersed throughout the dispersive medium under conditions of pressureand temperature existing in well fracturing, said slurry explosive beingnondispersible in well fluids over a time period required to fracturesuch formation, said method comprising:

injecting said slurry explosive into the well bore directly adjacentsaid formation through a tube extending from the surface through thewell bore to a level adjacent the formation, such that the slurry cannotcontact fluids in the well bore before reaching the formation;

placing a detonating device containing a high explosive charge withinthe slurry in the well bore; and

detonating said high explosive charge to explode theslurry,

thereby fracturing said formation.

4. A method as defined in claim 3 wherein said granular solid explosiveis one or more organic nitro compounds selected from the groupconsisting of RDX, HMX, PETN and TNT, and constitutes about between 35and 70 percent by weight of the slurry.

5. A method as defined in claim 4 wherein said dispersive medium isselected from the group consisting of water, alcoho], kerosene andhexane.

6. A method as defined in claim 4 wherein said dispersive medium iswater and said explosives constitute about between 45 and 70 percent byweight of the slurry.

7. A method as defined in claim 6 wherein said gelling agent is Carbopol941 and constitutes about 0.5 percent by weight of the slurry.

8. A method as defined in claim 3 wherein said dispersive mediumconstitutes about between 55 and 65 percent by weight of the slurry.

2. A method as defined in claim 1 wherein the detonating device includesa timer for detonating the high explosive charge after a presetinterval, and detonation of the high explosive charge is initiated bysaid timer.
 3. A method of fracturing a formation adjacent a well borewith a slurry explosive consisting essentially of a fluid dispersivemedium capable of desensitizing a granular explosive dispersed therein;one or more granular solid explosives which are organic nitro compoundsof high explosive power and which are nonhygroscopic and insoluble inthe dispersive medium, evenly dispersed throughout the dispersivemedium; and a gelling agent for maintaining the granular solid explosiveevenly dispersed throughout the dispersive medium under conditions ofpressure and temperature existing in well fracturing, said slurryexplosive being nondispersible in well fluids over a time periodrequired to fracture such formation, said method comprising: injectingsaid slurry explosive into the well bore directly adjacent saidformation through a tube extending from the surface through the wellbore to a level adjacent the formation, such that the slurry cannotcontact fluids in the well bore before reaching the formation; placing adetonating device containing a high explosive charge within the slurryin the well bore; and detonating said high explosive charge to explodethe slurry, thereby fracturing said formation.
 4. A method as defined inclaim 3 wherein said granular solid explosive is one or more organicnitro compounds selected from the group consisting of RDX, HMX, PETN andTNT, and constitutes about between 35 and 70 percent by weight of theslurry.
 5. A method as defined in claim 4 wherein said dispersive mediumis selected from the group consisting of water, alcohol, kerosene andhexane.
 6. A method as defined in claim 4 wherein said dispersive mediumis water and said explosives constitute about between 45 and 70 percentby weight of the slurry.
 7. A method as defined in claim 6 wherein saidgelling agent is Carbopol 941 and constitutes about 0.5 percent byweight of the slurry.
 8. A method as defined in claim 3 wherein saiddispersive medium constitutes about between 55 and 65 percent by weightof the slurry.